EXPERIMENTS IN EVOLUTION 



Mendel found that when pure-bred green-seeded peas were 

 crossed with pure-bred yellow-seeded peas, the offspring were all 

 yellow-seeded. When these hybrid plants were crossed with one an- 

 other, the following generation produced three yellow-seeded plants 

 to one green-seeded plant. (Illustration about half natural size.) 



Tower found that exposing the young stages of potato beetles to 

 extreme conditions of moisture and temperature produced in the fol- 

 lowing generations modifications that were inherited. The results of 

 high temperature and low humidity are illustrated at the left of the 

 parent type ; the results of low temperature and high humidity are 

 illustrated at the right. (Illustration about twice natural size.) 



